A variety of solid catalyst components comprising, as the indispensable ingredients, magnesium, titanium, halogen and electron donor have heretofore been proposed for catalysts. It is well known that the catalysts comprising the component of that type have high catalytic activity in olefin polymerization and that .alpha.-olefin polymers produced in the presence of the catalyst have high stereospecificity. In particular, it is known that the solid catalyst components comprising, as the electron donor, an aromatic ester such as typically a phthalate exhibit excellent capabilities. However, using aromatic compounds is often disliked as being not safe and not good for the health.
Regarding non-aromatic electron donors, a method of using an electron donor of a malonate derivative has been reported. For example, in Japanese Patent Publication (JP-B) Hei-4-80044, proposed were compounds of a general formula (II): ##STR2##
wherein either one or both of R.sup.3 and R.sup.5 are linear or branched hydrocarbon residues having 4 carbon atoms, or aromatic hydrocarbon residues. However, the stereospecificity of the polymers to be produced in the method in which the proposed compound is used is not good. In Japanese Patent Application Laid-Open (JP-A) Hei-6-122716, proposed are compounds of formula (II) in which R.sup.3 and R.sup.5 are bonded to each other to form a ring. In JP-A Hei-279517, proposed were compounds of formula (II) in which R.sup.4 and R.sup.5 are both hydrogens, those in which either one of R.sup.4 and R.sup.5 is a linear or branched hydrocarbon residue having 1 or more carbon atoms or an aromatic hydrocarbon residue, and the other is a hydrogen atom, and those in which R.sup.3 and R.sup.5 are both linear hydrocarbon residues having 2 or more carbon atoms. In the method in which the proposed compound is used, however, the yield of the polymers produced is extremely low. In JP-A Hei-8-157521, proposed were compounds of formula (II) in which R.sup.3 and R.sup.5 are both branched or cyclic hydrocarbon residues having 3 or more carbon atoms. In the method, however, the proposed malonates having branched or cyclic hydrocarbon residues are difficult to produce, and the yield of the polymers produced is low. Therefore, the method is not practicable. Other methods of using electron donors of other non-aromatic diesters were reported in JP-A Hei-3-124705 and JP-A Hei-3-168208. However, these methods are not always satisfactory for obtaining stereospecific polymers at high yields.